A "yes" vote in the Scottish independence referendum would be "cataclysmic" for the West, and would threaten the stability of the wider world, the former secretary general of Nato, Lord Robertson, has said.

Speaking to an audience at the Brookings Institution, a Washington-based think-tank, Lord Robertson said the "loudest cheers" for Scottish independence would be from the UK's "adversaries and from our enemies."

Lord Robertson, who was the tenth Secretary General of Nato, between October 1999 and early January 2004, said a "debilitating divorce" after a "yes" vote in September could threaten wider global stability and have far-reaching geopolitical implications in increasingly uncertain times.

The former Labour politician told the audience: "This is not a purely domestic matter, even though it's a decision that will be taken by the Scottish people." He said a "yes" vote would leave the United Kingdom a "diminished country whose global position would be open to question".

Nicola Sturgeon, Scotland's Deputy First Minister, told the BBC she was "shocked" by the language of the former Labour defence secretary's speech, and the Scottish government condemned the comments as "crass and offensive".

Lord Robertson also called on the US government and other UK allies to make their views on the referendum public as an independent Scotland would "affect them as well".

In the speech delivered last night Lord Robertson said: "The loudest cheers for the break-up of Britain would be from our adversaries and from our enemies.

"For the second military power in the west to shatter this year would be cataclysmic in geo-political terms."

"This is not a purely domestic matter even though it's a decision that will be taken by the Scottish people."

"The Scottish people need to be conscious that they are taking a decision, not just for themselves and for future generations in a one-off vote, but that it also has an effect elsewhere and people who are affected, or think they will be affected, have every right to speak out," he added.

Lord Robertson also took issue with some of the reasons given for independence by the 'Yes' camp: "Scotland is not a colony, it is not oppressed, it is not discriminated against it isn't disadvantaged," he said.

"Indeed it's the second most prosperous part of the United Kingdom outside of London and the South East of England, and that is largely because we are part of the United Kingdom."

"We [Scots] are not persecuted, Scots are prominent, some would say dominant at every level in British life. We speak the same language, we enjoy the same currency, the same central bank, the same regulatory system, the same public service broadcaster and much much more", he added.

A spokesman for Alex Salmond, who is currently also in the US on a five day trade mission, told the BBC the comments were "disappointing but not surprising".

"Lord Robertson once claimed having a Scottish Parliament would kill demand for independence stone dead - with comments like this it is the No campaign that will continue to sink like a stone," they said.